LABORATORY CONTROLLED STUDIES ON SOME INTERACTIONS BETWEEN CLAY MINERALS AND LIVING ORGANISMS: A PERSPECTIVE ON WEATHERING FROM MOBILITY OF SEVERAL NON-ESSENTIAL METALS

In studies of mobility of metals in systems of association between clay minerals and living organisms, reports are very few on non-essential metals in comparison to that on the essential metals. To get some useful clues to the processes of mobility of metals in living organism-facilitated weathering environments, laboratory controlled studies were made on the mobility of several non-essential metals in two separate associations between earthworms and smectite clay minerals and in associations between radish plants and smectite and illite clay minerals. The non-essential minerals considered in these studies included Rb, Sr, U, Th, and rare-earth elements. As expected, the clays in associations the earthworms and the plants yielded considerably much higher amounts, by as much as times, of water extractable metals than the clays without such living entities. For example, a batch of smectite digested by earthworms yielded 1,645 micrograms of total water dissolved metals per gram of the clay mass, whereas the same clay but without any earthworm activities had 327 micrograms of total water dissolved metals per gram of the clay. The activities of the living organisms caused differential mobilities among some geochemically similar metals. The activities caused the water extractable phase to have an increase in the K/Rb ratio, but to have varied changes in the U/Th and La/Yb ratios, and to have almost no change in the Sr/Ca ratio. The collective data of the non-essential metals from the associations of the clay mineral and the plants or the earthworms suggest that organic cycling of metals leaves a very strong impression on chemical signatures of the surface and ground waters and that studies of water geochemistry in a drainage basin for the purpose of monitoring climatic change would greatly benefit from a consideration of change in the system of living organisms within the basin.